Before menstruation, you may gain weight slightly, which is caused by changes in hormone levels in your body, and will naturally return to normal after menstruation is over. Before menstruation, the corpus luteum of the ovary has not yet atrophied and is still secreting progesterone. Under the action of progesterone, water and sodium ions in the female body can be retained in the interstitial space of the tissues, which leads to an increase in body weight, usually between 0.5 and 1 kg, so the weight may become heavier before the onset of menstruation. When the female corpus luteum completely atrophied after the onset of menstruation, at this time the female body progesterone levels drop to a minimum, after the loss of progesterone, excess water and sodium can be discharged out of the body, the end of the menstrual period after the weight back to normal. When a woman’s weight increases abnormally, she should consult a doctor to clarify the cause of the disease, so as not to delay the disease and lead to adverse consequences.